Formation of nitrated naphthalene in the sulfate radical oxidation process in the presence of nitrite.

Polycyclic aromatic hydrocarbons (PAHs) have become a global environmental concern due to their potential hazardous implication for human health. In this study, we found that sulfate radical (SO) could effectively degrade naphthalene (NAP), a representative PAH in groundwaters, generating 1-naphthol. This intermediate underwent further degradation, yielding ring-opening products including phthalic acid and salicylic acid. However, the presence of nitrite (NO), a prevalent ion in subsurface environments, was observed to compete with NAP for SO, thus slowing down the NAP degradation. The reaction between NO and SO generated a nitrogen dioxide radical (NO). Concurrently, in-situ formed 1-naphthol underwent further oxidization to the 1-naphthoxyl radical by SO. The coupling of 1-naphthoxyl radicals with NO gave rise to a series of nitrated NAP, namely 2-nitro-1-naphthol, 4-nitro-1-naphthol, and 2,4-dinitro-1-naphthol. In addition, the in-situ formed phthalic acid and salicylic acid also underwent nitration, generating nitrophenolic products, although this pathway appeared less prominent than the nitration of 1-naphthol. When 10 μΜ NAP was subjected to heat activated peroxydisulfate oxidation in the presence of 10 μΜ NO, the total yield of nitrated products reached 0.730 μΜ in 120 min. Overall, the presence of NO dramatically altered the behavior of NAP degradation by SO oxidation and contributed to the formation of toxic nitrated products. These findings raise awareness of the potential environmental risks associated with the application of SO-based oxidation processes for the remediation of PAHs-polluted sites in presence of NO.